Gallium nitride (GaN)-based devices are increasingly implemented in high-power application such as power switching devices and wireless base stations. Another example of a GaN-based device is a GaN high-electron-mobility transistor (HEMT) amplifier, which have low on-resistance, high-off breakdown voltages, and the ability to handle large current. GaN-based enhancement-mode devices operate in a similar manner to silicon-based MOSFET devices by being normally off in a non-conducting state. However, conventional GaN-based enhancement-mode transistors typically have threshold voltage (Vth) uniformity issues, which leads to unreliable device performance.